Re:Re:[PATCH 6/6] irq: Potentially 'offset out of size' bug

From: Thomas Gleixner
Date: Tue Sep 14 2021 - 08:27:10 EST

On Tue, Sep 14 2021 at 08:48, Jiasheng Jiang wrote:
>> On Fri, Sep 10 2021 at 03:26, Jiasheng Jiang wrote:
>> The find_next_bit() use nr_irqs as size, and using it without
>> any check might cause its returned value out of the sizei
> On Fri, Sep 10 2021 at 18:28, tglx wrote:
>> Why exactly is this a problem? The return value has to be checked at the
>> call site anyway.
> There is really a check at the call site, but the annotation of the
> irq_get_next_irq() is 'Returns next irq number after offset or nr_irqs
> if none is found', which tells the programmer should not check the
> return value of it. In case of a programmer write a new call for the
> irq_get_next_irq(), he may not check the return value because of the
> annotation said.

The return value has always to be checked because nr_irqs is guaranteed
to be an invalid index.

> Therefore, it had better to add the check inside of irq_get_next_irq()
> to fit for the annotation.

Care to look what find_next_bit(..., size) does?

* Returns the bit number for the next set bit
* If no bits are set, returns @size.

So for:

res = find_next_bit(addr, size, offset);

res is guaranteed to be:

offset < res <= size

IOW. irq_get_next_irq() is doing exactly what the comment says.

So again, which problem are you trying to solve?